Hmm lets see my probably bias opinion, I should mention that only recently did I start buying new hardware it used to be a lucky dip of what I would get in second hand/free land.
Gigabyte - If I buy a new board it is Gigabyte always Gigabyte even though I could have ended up with an ASUS board when I started buying new boards but I got a Gigabyte board because G31M-S2L was the most expensive one my sister would by for my birthday.
I also previously had liked my Gigabyte mATX Socket 370 board (cant remember what it is except it is intel815), it also happens that I have a Super Socket 7 Board that works well to except its pickness with some RAM and AGP Cards but other then that no problems with Gigabyte boards whatsoever. The only dead one I have had has always been dead so nothing to change my mind there.
Gigabyte also uses Award BIOS which I prefer over AMI BIOS since I don't like the look, I can also see me disliking UEFI because of simplified mouse controlled yuckyness (hmm maybe thats exaggeration, I dunno).
MSI - I consider them second to Gigabyte, I like the MSI boards I have encountered just not as much as Gigabyte mostly due to bias and that my mATX Socket 370 had onboard NIC and the MSI boards I encountered/had didn't which is an incredibly stupid reason especially considering the Socket 478 Gigabyte board that I got that didn't have it. Although that wasn't as bad as an LGA775 (I think) board with a P4 2.8 that didn't have onboard NIC I just couldn't understand why it was an intel board I think.
DFI - Have a Socket 478 DFI board no idea about what it is, seemed to work fine, I guess I haven't really used it terribly much it has AWARD BIOS which is automatically a plus but I doubt I would buy a DFI board when they are so expensive.
eVGA - Sound nice, AWARD BIOS, but very expensive.
Jetway - I have a socket 7 board which I use as my linux firewall which has been running fine for the last 4 years or so I think.
ASUS - Uses AMI BIOS so I avoid however I gather there boards work reasonably well.
SOLTEK - Can't really give an oppionion here but the only board I've ever had contained bad capacitors.
Intel - For some reason I just despise these boards because I think to do with not detecting certain HDDs after a while. (this wasn't at home, somewhere else) Also AMI BIOS and less options are offputting.
OEM (Compaq) - OEM boards are just horrible why why why why do I have 6 compaq (ugh its 6) boards of which only one has a decent AWARD BIOS, one is a Windows 3.1 like BIOS, and the other 4 seemed a pretty horible limited like AMI BIOS but horribler I think, If there was only a way to atleast go to an Intel AMIBIOS I would be happier particularly if I could get rid of that stupid splash screen. The board with the AWARD BIOS has a lot of bad caps but it still seems to work fine but argh no AGP same with the other compaq Socket 370 board (I didn't intend this to be a compaq rant).
The compaq deskpro 4000 is alright unless I ever have to replace that psu which has the AT power connectors and some other plug and a different sort of on switch (no 240V AC to the front of the case).
And onboard NIC which is always nice particularly when its a socket 7 board.
OEM (Other) - Had 2 Acer's one a socket 7 board which still goes well, no problems there and an Acer V80M (Slot 1, was so cheap I thought didn't even have plastic around the IDE connectors, well thats what I thought anyway) which was my first experience of bad capacitors and is why I am absolutely paranoid when a computer freezes because I remember having freezes all the time caused by the bad caps. An interesting fact was that UT would freeze when using DirectX3D but not with OpenGL.
Only had 3 other OEM board I think a Packard Bell 486 which had 98FE on it for who knowes what reason was pretty slow to start up I remember but it was 98 not 95 so obviously it must be better right? This is probably the time to admit to the fact we used Windows 3.1 up until 2000. And I belive my uncle got the Acer Pentium MMX 166 from the computer fair with 95B on it. It even had a 1 year warranty when it was a second hand computer, they don't make second hand computers like that anymore. I'm not sure how that actually is relevent but interesting anyway. So the packard Bell one was ok not really fussed I htink I had a digital 486 (i think that was what it was) that I couuld never get to work. Lastly have a Celeron 400 HP box which is so small has a real AMI BIOS so better then some options but glad I never had to use it I used the Acer V80M instead at the time.
Woah this was quite abit longer then I thought, ECS, Asrock I haven't touched either but I vaugly thought they had AMI BIOS so I run away from those I think.